88 Milton Landowne 



Brandfonbrener and Shock, 1955) in similar manner for the 

 average decrease with age in total oxygen consumption, and 

 carbon dioxide production (Shock and Yiengst, 1955), or for 

 estimates of total intracellular water (Shock, Watkin and 

 Yiengst, 1955), based on data which have been reported for 

 similar but less rigidly selected groups of subjects in studies 

 from our laboratory (Table II). These indices all decrease by 



Table II 



The relation between cardiac stroke int. ex and age for 67 "normal" 

 men. comparison of 2 groups of subjects suggests that the increase 

 in vascular resistance exceeds the decrease in indices of overall 



metabolism. 



less than 0-6 ±0-12 per cent per year. Considering these 

 items as general indices of the reduction in metabolically 

 active tissue, the greater average increase in vascular resistance 

 indicates a reduction in the generosity of cellular perfusion. 

 This further suggests that overall, and on the average, the 

 changes in metabolic activity and protoplasmic mass may be 

 consequences of circulatory attrition; for if these changes 

 occurred pari passu, or if cellular alterations were to be con- 

 sidered primary to reduction in circulation, it would not be 

 likely that the decrease in perfusion would exceed evidences of 

 reduction in cellular activity. These evidences for primary 

 vascular alteration are intended to apply to the total circula- 

 tion generally, for in any one circulatory region, circumstances 

 may be quite different. From studies on renal blood flow 

 (Davies and Shock, 1950), and resistance (Landowne and 

 Shock, 1951), which have been carried out in our laboratory, 



